Dumbbell



FIG. 1 is a front, top, right side perspective view of the dumbbell;

FIG. 2 is a front view of a dumbbell; and,

FIG. 3 is a right side view of a dumbbell.

The rear view is the same as the front view of FIG. 2 and the left side, top and bottom side views are the same as the right side view of FIG. 3. 

The ornamental design for a dumbbell, as shown and described. 